Self-inflating tire

ABSTRACT

A self-inflating tire assembly includes an air tube connected to a tire and defining an air passageway, the air tube being composed of a flexible material operative to allow an air tube segment opposite a tire footprint to flatten, closing the passageway, and resiliently unflatten into an original configuration. The air tube is sequentially flattened by the tire footprint in a direction opposite to a tire direction of rotation to pump air along the passageway to an inlet device for exhaust from the passageway or to an outlet device for direction into the tire cavity. The inlet device is positioned within the annular passageway 180 degrees opposite the outlet device such that sequential flattening of the air tube by the tire footprint effects pumping of air along the air passageway with the tire rotating in either a forward or reverse direction of rotation. The invention further includes an outlet device for regulating the tire cavity pressure and flow into the cavity.

FIELD OF THE INVENTION

The invention relates generally to self-inflating tires and, morespecifically, to a pump mechanism for such tires.

BACKGROUND OF THE INVENTION

Normal air diffusion reduces tire pressure over time. The natural stateof tires is under inflated. Accordingly, drivers must repeatedly act tomaintain tire pressures or they will see reduced fuel economy, tire lifeand reduced vehicle braking and handling performance. Tire PressureMonitoring Systems have been proposed to warn drivers when tire pressureis significantly low. Such systems, however, remain dependant upon thedriver taking remedial action when warned to re-inflate a tire torecommended pressure. It is a desirable, therefore, to incorporate aself-inflating feature within a tire that will self-inflate the tire inorder to compensate for any reduction in tire pressure over time withoutthe need for driver intervention.

DEFINITIONS

“Aspect ratio” of the tire means the ratio of its section height (SH) toits section width (SW) multiplied by 100 percent for expression as apercentage.

“Asymmetric tread” means a tread that has a tread pattern notsymmetrical about the center plane or equatorial plane EP of the tire.

“Axial” and “axially” means lines or directions that are parallel to theaxis of rotation of the tire.

“Buffer volume” means the pump minimum volume.

“Chafer” is a narrow strip of material placed around the outside of atire bead to protect the cord plies from wearing and cutting against therim and distribute the flexing above the rim.

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection.

“Equatorial Centerplane (CP)” means the plane perpendicular to thetire's axis of rotation and passing through the center of the tread.

“Footprint” means the contact patch or area of contact of the tire treadwith a flat surface at zero speed and under normal load and pressure.

“Inboard side” means the side of the tire nearest the vehicle when thetire is mounted on a wheel and the wheel is mounted on the vehicle.

“Lateral” means an axial direction.

“Lateral edges” means a line tangent to the axially outermost treadcontact patch or footprint as measured under normal load and tireinflation, the lines being parallel to the equatorial centerplane.

“Net contact area” means the total area of ground contacting treadelements between the lateral edges around the entire circumference ofthe tread divided by the gross area of the entire tread between thelateral edges.

“Non-directional tread” means a tread that has no preferred direction offorward travel and is not required to be positioned on a vehicle in aspecific wheel position or positions to ensure that the tread pattern isaligned with the preferred direction of travel. Conversely, adirectional tread pattern has a preferred direction of travel requiringspecific wheel positioning.

“Outboard side” means the side of the tire farthest away from thevehicle when the tire is mounted on a wheel and the wheel is mounted onthe vehicle.

“Peristaltic” means operating by means of wave-like contractions thatpropel contained matter, such as air, along tubular pathways.

“Peristaltic pump tube” means a tube formed or molded in a tire or anembedded tube which may be inserted post cure or pre-cure.

“Pump minimum volume” or “buffer volume” means the smallest value of thepump variable volume.

“Pump maximum volume” means the volume of fluid located between theperistaltic pump tube inlet and the outlet valve.

“Pump variable volume” means the volume of fluid located between thepinched tube path and the entry of the outlet valve.

“Radial” and “radially” means directions radially toward or away fromthe axis of rotation of the tire.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is an isometric view of the valve, tube and filter for aperistaltic pump assembly.

FIG. 2 is a side view of the assembly of FIG. 1 shown mounted in a tire.

FIG. 3 is an enlarged partial cross sectional view of the tire and rimassembly with the pump valve mechanism shown mounted in the tire.

FIG. 3A is an enlarged perspective view of the pump valve mechanism ofFIG. 3.

FIG. 4 is a perspective view of a first embodiment of a regulatormechanism of the present invention.

FIG. 5 is a partial section view through the regulator mechanism of FIG.4 in the direction 5-5.

FIGS. 6 and 7 are cross-sectional views of the regulator mechanism inoperation, in the closed position and the open position, respectively.

FIG. 8 is a perspective view of a second embodiment of a regulatormechanism of the present invention shown in a first position.

FIG. 9 is perspective view of the regulator mechanism of FIG. 8 shown ina second position.

FIG. 10 is a perspective view of the adjustable cap of the regulatormechanism of FIG. 8.

FIG. 11 is a perspective view of a second embodiment of a pump system ofthe present invention.

FIGS. 12A and 12B illustrate front views of an interchangeable valvebody.

FIGS. 13A, 13B and 13C represent an illustration of the pump maximumvolume, the pump variable volume, and the buffer or pump minimum value.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 through 3, a tire assembly 10 includes a tire 12, aperistaltic pump assembly 14, and a tire rim 16. The tire mounts in aconventional fashion to a pair of rim mounting surfaces 18 locatedadjacent outer rim flanges 20. The outer rim flanges 20 have an outerrim surface 22 that engages the bead area of the tire. The tire is ofconventional construction, having a pair of sidewalls 30 extending fromopposite bead areas 34 to a crown or tire tread region 38. The tire andrim enclose a tire cavity 40.

As shown in FIGS. 1-2, the peristaltic pump assembly 14 includes a pumptube 42 that is mounted in a tire passageway 44, which is preferablylocated in the sidewall area of the tire, preferably near the beadregion. The tire passageway is preferably molded into the sidewall ofthe tire during vulcanization and is preferably annular in shape. Thepump tube 42 has a first end 42 a joined together by an inlet device 46and a second end 42 b joined together with an outlet device 50. The pumptube 42 is comprised of a tube formed of a resilient, flexible materialsuch as plastic, silicone, elastomer or rubber compounds, and is capableof withstanding repeated deformation cycles when the tube is deformedinto a flattened condition subject to external force and, upon removalof such force, returns to an original condition generally circular incross-section. The tube is of a diameter sufficient to operatively passa volume of air sufficient for the purposes described herein andallowing a positioning of the tube in an operable location within thetire assembly as will be described. Preferably, the tube has a circularcross-sectional shape, although other shapes such as elliptical or lensshape may be utilized. Alternatively, the passageway 44 molded or formedinto the tire sidewall may serve as the pump tube 42.

As shown in FIG. 2, the inlet device 46 and the outlet device 50 arespaced apart a desired distance typically in the range of approximately90 degrees or more, typically about 180 degrees to 360 degrees. If 180degrees is selected, two 180 degree pumps may be used. The inlet andoutlet device may be located adjacent each other, thus forming a single360 degree pump. Other variations may be utilized, such as 270 degrees,etc.

The inlet device 46 in its simplest form may be the inlet tube endexposed to the atmosphere. The inlet device may optionally comprise acheck valve and/or an optional filter. The outlet device 50 is apressure and flow regulating device, and regulates the tire cavitymaximum pressure. The outlet device 50 also functions to regulate theflow into and out of the tire cavity. The outlet device is described inmore detail, below.

As will be appreciated from FIG. 2, the inlet device 46 and the outletdevice 50 are in fluid communication with the circular air tube 42. Asthe tire rotates in a direction of rotation 88, a footprint 100 isformed against the ground surface 98. A compressive force 104 isdirected into the tire from the footprint 100 and acts to flatten asegment 110 of the pump 42. Flattening of the segment 110 of the pump 42forces a portion of air located between the flattened segment 110 andthe outlet device 50, in the direction shown by arrow 84 towards theoutlet device 50. The portion of air will then regulated through theoutlet device 50. If the pressure at the inlet of the outlet device issufficiently high, the internal valve will open and fill the tirecavity, as described in more detail, below.

As the tire continues to rotate in direction 88, the previouslyflattened tube segments 110, 110′, 110″ will be sequentially refilled byatmospheric air flowing into the inlet device 46 along the pump tube 42.The inflow of air from the inlet device 46 continues until the outletdevice 50 rotating counterclockwise as shown with the tire rotation 88,passes the tire footprint 100.

The location of the peristaltic pump assembly will be understood fromFIGS. 2-4. In one embodiment, the peristaltic pump assembly 14 ispositioned in the tire sidewall, radially outward of the rim flangesurface 26 in the chafer 120. So positioned, the air tube 42 is radiallyinward from the tire footprint 100 and is thus positioned to beflattened by forces directed from the tire footprint as described above.The segment 110 that is opposite the footprint 100 will flatten from thecompressive force 114 from the footprint 100 pressing the tube segmentagainst the rim flange surface 26. Although the positioning of the tube42 is specifically shown as between a chafer 120 of the tire at the beadregion 34 and the rim surface 26, it is not limited to same, and may belocated at any region of the tire such as anywhere in the sidewall ortread. The diametric sizing of the peristaltic pump air tube 42 isselected to span the circumference of the rim flange surface 26.

Pressure Regulating Outlet Device

The regulator device 50 is a pressure and flow regulating device, andregulates the tire cavity maximum pressure. The regulator device 50 alsofunctions to regulate the flow into and out of the tire cavity. Theregulator device has a valve body 52 having a first end 53 that has avalve passageway 54 that extends from the first end to a second end 56.The first end of the valve body 52 is mounted through the tire sidewallas shown in FIGS. 3, 3A so that the valve passageway 54 is in fluidcommunication with the tire cavity 40. The valve passageway 54 has anexpanded portion 58 and a narrow portion 60. A large ball 62 is receivedin the expanded portion 58 and positioned for engagement with the narrowportion 60. A spring 64 is positioned within the valve passageway forengagement with the ball 62. The spring 64 biases the ball intoengagement with the narrow portion 60, so that flow is blocked in theinterior passageway 54.

The second end 56 of the valve body has an outer threaded portion 57that is received within a first threaded end 70 of an adjustable housing72. The adjustable housing has an internal cavity 74 that extends fromthe first threaded end 70 to the second threaded end 76. The internalcavity 74 has a fixed buffer volume portion and an adjustable buffervolume portion. The fixed volume portion is defined by the non-threadedinner wall of the internal cavity having a length C. The fixed volume isequal to the cross-sectional area of the internal cavity times thelength C. The adjustable volume portion is defined by the amount of thethreaded length that is exposed within the internal cavity and isindicated as distance B. The adjustable volume is determined from thedistance B times the cavity cross-sectional area. The distance B may bezero if the valve body is fully received within the adjustable housing.The adjustable housing and respective internal buffer volumes may bemodified by substituting the adjustable housing as shown in FIG. 12 A inorder to increase the fixed buffer volume or by substituting theadjustable housing as shown in FIG. 12 b in order to decrease the fixedbuffer volume.

The regulator device 50 further comprises an elbow fitting 80 having afirst end 82 connected to the adjustable housing inlet end 76 and asecond end 84 connected to the pump tube outlet 42 b. The second end ofthe elbow fitting 80 may comprise a flared fitting 86.

The maximum air pressure delivered by the peristaltic pump can be fixedby setting the volume of the pump tube and the buffer volume locatedbetween the end of the tube and the check valve and the adjustablebuffer chamber. The pump tube volume is selected by design with the tubedimensions and the tube length. As shown in FIG. 11, multiple pump tubesmay be used, with the selection of the tube length and inner tubedimensions to tune the system. The buffer or dead volume can also be setby design. The air in the buffer volume chamber is not compressed, butfunctions to tune or adjust the maximum air pressure of the pump system.The buffer volume acts as a storage chamber for accumulating air massfor transfer to the tire cavity. Increasing the buffer volume willdecrease the tire pressure, while decreasing the buffer volume willincrease the tire cavity pressure. Thus, by adjusting the buffer volume,one can adjust the desired tire final pressure.

The operation of the system and the outlet device 50 can now bedescribed. As shown in FIG. 2, the tire rotates in a direction ofrotation 88, and a footprint 100 is formed against the ground surface98. A compressive force 104 is directed into the tire from the footprint100 and acts to flatten a segment 110 of the pump 42. Flattening of thesegment 110 of the pump 42 forces a portion of air located between theflattened segment 110 and the regulator device 50, in the directionshown by arrow 84 towards the outlet device 50. The portion of air willthen be regulated through the outlet device 50. If the pressure at theinlet 86 of the regulator device is sufficiently high, the fluidpressure will overcome the spring pressure 54 (cracking pressure), thusopening the internal check valve. Thus fluid from the pump outlet 42 bwill flow into the elbow fitting 80 and into the adjustable housing 72.

If the pressure in the pump tube 42 b is less than the tire pressure,the ball 62 will engage the narrow portion 60 and block flow from eitherdirection. The check valve 62 when closed, blocks flow fromcommunicating from the pump 42 b into the tire cavity 40, and alsoprevents back flow from the tire cavity into the pump 42. When the checkvalve is closed, the pump compresses the air in the pump tube 42. Airfrom the pump tube enters the elbow fitting 80 of the regulator device,and then enters the buffer volume chamber 74. The buffer volume chamberwill fill while the check valve remains closed. When the pressure in theinlet 56 of the regulator device exceeds the cracking pressure, thecheck valve opens and will allow air from the pump to fill the tirecavity. The check valve will close when the inlet pressure P_(T) fallsbelow the cracking pressure. The cycle of opening and closing the checkvalve will allow the tire cavity to be filled as the tire rotates aspecified distance. A maximum tire cavity will be reached based upon thepump volume and the buffer volume. The buffer volume may be adjusted byturning the valve body 52 relative to the adjustable housing. Increasingthe buffer volume results in a decrease of tire final pressure, whiledecreasing the buffer volume results in an increase of the tire finalpressure. The advantage of having an adjustable buffer volume allows themaximum system pressure of the tire cavity to be tuned for a specifictire.

FIGS. 8-10 illustrate a second embodiment of a pressure regulator 200.The pressure regulator 200 comprises a valve body 202 having an internalpassageway 204 that extends through the valve body 202. The internalpassageway 204 includes a movable check valve assembly 206. The movablecheck valve assembly includes a ball 208, a spring 210 housed within areceptacle 212. The receptacle has a retainer 214 which retains the ball208 within the check valve assembly. The outer edge of the receptaclemay have external threads like a screw, so that the receptacle may bescrewed into or out of the internal passageway 204. A variable buffervolume 220 is located adjacent the movable check valve assembly, so thatwhen the movable check valve assembly is rotated clockwise, the variablebuffer volume decreases. The outer receptacle of the check valve mayhave notations on it to indicate to a user to indicate the relationshipof the number of turns to the volume adjustment. Alternatively, themovable check valve may slide within the passageway 204, with retainingmeans located within the passageway which allow the position of themovable check valve to be repeatedly adjusted and then fixed inposition.

The valve body 202 of the pressure regulator 200 further comprises asecond portion 222 which is at right angles to the first portion 224 ofthe valve body. The second portion has an interior fixed dead volume 230which is in fluid communication with the variable volume 220. Locatedadjacent the interior fixed dead volume 230 is an outlet 240. The outlet240 is connected to the pump tube outlet 42 b. The second portion 222 ismounted in the tire, typically in the sidewall and connected to the pumptube outlet 42 b. The first portion 224 of the valve body is mountedthrough the sidewall and into the tire cavity 40.

The operation of the system and the outlet device 200 can now bedescribed. As shown in FIG. 2, the tire rotates in a direction ofrotation 88, and a footprint 100 is formed against the ground surface98. A compressive force 104 is directed into the tire from the footprint100 and acts to flatten a segment 110 of the pump 42. Flattening of thesegment 110 of the pump 42 forces a portion of air located between theflattened segment 110 and the regulator device 200, in the directionshown by arrow 84 towards the outlet device 200. The portion of air willthen be regulated through the outlet device 200. If the pressure at theinlet of the regulator device is sufficiently high, the fluid pressurewill overcome the spring pressure (cracking pressure), thus opening theinternal check valve. Thus fluid from the pump outlet 42 b will flowinto the regulator and out into the tire cavity through a hole in theadjustable check valve assembly.

If the pressure in the pump tube 42 b is less than the tire pressure,the ball 208 will engage the narrow portion 214 and block flow fromeither direction. The check valve when closed, blocks flow fromcommunicating from the pump 42 b into the tire cavity 40, and alsoprevents back flow from the tire cavity into the pump 42. When the checkvalve is closed, the pump compresses the air in the pump tube 42. Airfrom the pump tube enters the regulator device, and fills the buffervolume chambers 220,230. When the pressure to the inlet of the regulatordevice exceeds the cracking pressure, the check valve opens and willallow air from the pump to fill the tire cavity. The check valve willclose when the inlet pressure P_(T falls) below the cracking pressure.The cycle of opening and closing the check valve will allow the tirecavity to be filled as the tire rotates a specified distance. A maximumtire cavity will be reached based upon the pump volume and the buffervolume. The buffer volume may be adjusted by turning the adjustablecheck valve relative to the housing. Increasing the buffer volumeresults in a decrease of tire final pressure, while decreasing thebuffer volume results in an increase of the tire final pressure. Theadvantage of having an adjustable buffer volume allows the maximumsystem pressure of the tire cavity to be tuned for a specific tire.

The table below indicates exemplary tires, all having the same internaltire volume of 38 L and initial tire pressure of 1.8 Bar. All of theexemplary pumps have a circumferential length of 180 degrees. Examples 1and 2 have a pump size of 2×1 with a pump volume of 1036 mm3. Forexample 1 the buffer volume is selected to be 459 mm3, resulting in adesired final tire pressure of 2.2 bar. A distance of 241 km is neededto achieve the final tire pressure. If the buffer volume is decreased to351 mm3, with all other variables being equal, the final tire pressurewill be 2.9 bar (Ex. 2) as compared to 2.2 bar for Ex. 1. A longerdistance of 490 km will be needed to achieve a higher final tirepressure of 2.9 bar.

Examples 3 and 4 illustrate a smaller tube size resulting in a smallerpump volume of 700 mm3. For a buffer volume of 310 mm3 (Ex 3) results ina final tire pressure of 2.2 bar and a needed distance of 355 km toachieve the final tire pressure. Ex 4 illustrates all the properties ofEx. 3, except for a smaller buffer volume of 237 mm3, resulting in ahigher final tire pressure of 2.9 bar achieved in 727 km.

Examples 5-8 have the same properties as examples 1-4, with example 5corresponding with example 1, etc. the cracking pressure of the valve ishigher for examples 5-8 as compared to 1-4. A slightly lower buffervolume is needed in examples 5-8 to achieve the same final tire pressureas examples 1-4. The higher cracking pressure also results in asignificantly shorter distance to be traveled by the pump/tire in orderto result in the final tire pressure. The volume ratios of the buffervolume to pump volume may be used to determine a new buffer volumeshould the pump volume or cavity volume change. The buffer volume may beadjusted by rotating screw 66. The number of turns of the screw (e.g. 5turns) would result in a distance of 4 mm with a screw pitch of 75 mm.

Cavity A B C D Cracking Volume Tire Initial Tire Buffer Volume FinalTire Needed Volumes Pressure Angle Size [mm3] Volume pressure [mm3]pressure Distance Ratio 0.1 bar 180 2 × 1 1036 38 L 1.8 bar 459 2.2 bar241 km 0.443 180 2 × 1 1036 38 L 1.8 bar 351 2.9 bar 490 km 0.339 1802.7 × 0.5 699.5 38 L 1.8 bar 310 2.2 bar 355 km 0.443 180 2.7 × 0.5699.5 38 L 1.8 bar 237 2.9 bar 727 km 0.339 0.3 bar 180 2 × 1 1036 38 L1.8 bar 422 2.2 bar 137 km 0.407 180 2 × 1 1036 38 L 1.8 bar 329 2.9 bar324 km 0.318 180 2.7 × 0.5 699.5 38 L 1.8 bar 285 2.2 bar 203 km 0.407180 2.7 × 0.5 699.5 38 L 1.8 bar 222.5 2.9 bar 485 km 0.318

The maximum air pressure delivered by a peristaltic pump embedded in atire can be fixed by setting the right volume of the pump tube and thebuffer volume. The pump tube volume can be set by design with thedimensions of the tube sections and tube length. The buffer volume canalso be set by design but can also be easily manually changed by themean of a dedicated device or by interchanging appropriate parts beforethe valve. This can be implemented with either a set of tube withdifferent lengths or a set of small tanks to be inserted before thevalve.

Variations in the present invention are possible in light of thedescription of it provided herein. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention. It is, therefore, tobe understood that changes can be made in the particular embodimentsdescribed which will be within the full intended scope of the inventionas defined by the following appended claims.

What is claimed is:
 1. A self-inflating tire assembly comprising: a tiremounted to a rim, the tire having a tire cavity, first and secondsidewalls extending respectively from first and second tire bead regionsto a tire tread region; an air tube connected to the tire and beingcomposed of a flexible material operative to allow a portion of the airtube segment near a tire footprint to substantially open and close theair tube, a regulator device connected to an end of the air tube, theregulator device includes an elbow fitting mounted in the tire sidewall,the elbow fitting having a first end for connecting to an end of the airtube and a second end for connecting to a first end of an adjustablehousing, said adjustable housing having a buffer volume therein definedby a movable wall, said movable wall being connected to a valve body,wherein the valve body has an outer threaded surface that is receivedwithin the adjustable housing.
 2. The self-inflating tire assembly ofclaim 1 wherein the volume of the buffer chamber is adjustable.
 3. Theself-inflating tire assembly of claim 1 wherein the buffer chamber hasan adjustable outer wall.
 4. The self-inflating tire assembly of claim 1wherein the buffer chamber is formed in the void formed by a threadedfastener mounted in a chamber.
 5. The self-inflating tire assembly ofclaim 1 wherein the regulator device is mounted in the tire cavity. 6.The self-inflating tire assembly of claim 1 wherein the inlet regulatordevice is mounted in the tread of the tire.
 7. The tire assembly ofclaim 1, wherein the air tube is sequentially flattened by the tirefootprint to pump air along the air passageway in either a forward tiredirection of rotation or a reverse tire direction of rotation.
 8. Thetire assembly of claim 1, wherein the pump inlet and the regulatordevice are mounted to the annular air tube substantially 180 degreesapart.
 9. The tire assembly of claim 1, wherein the pump inlet and theregulator device are mounted to the annular air tube substantially 360degrees apart.
 10. The tire assembly of claim 1, wherein thecross-sectional shape of the air tube is elliptical.